An electroless method of forming high aspect ratio metal particles includes the steps of mixing a metal or metal salt with at least one acid to form an acidified metal halide salt solution, and mixing the solution with a supersaturated sol to form a sol comprising solution. Metal cations provided by the acidified metal salt are reduced to form a plurality of high aspect ratio metal particles. Instead of using a sol, an organic compound can be oxidized to generate the reducing agent. A metal comprising particle assembly includes a plurality of high aspect ratio metal platelets having an aspect ratio of a major dimension averaging from 10 to 200 times a nanoscale minor dimension of the platelet. The platelets can be used for nail polish, eye liner or the cores for medical delivery vehicles.